THE SMOOTH SOUNDING GRAPH. A Manual for Field Work ... - BGR

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41 cable drums. Rewinding it on the drums can be done either by hand or by an electro-motor driven by the car batteries. Depending on the surface conditions pulling the current cables very often is a hard work in case of L/2-distances >300m. This difficulty can be overcome by adding additional drums brought to A and B by car. Con- necting them to the ends of the first cables has to be done carefully with respect to the insulation. This is a really "weak point". We must be sure that there will be no "leakage" of current. Finally it should be mentioned that the unpolarisable potential electrodes (see chapter 1.6) are to be transported - all four of them - within a big plastic bottle filled with a saturated solution of copper sulphate. Thus the porous porcelain is sur- rounded by the fluid from in- and outside and cannot dry out. In any case the electrodes have to be controlled before starting the next measurement that there is enough fluid inside and no crust outside in order to get a good contact to the ground within the "holy" district.
42 2.2. Possible errors influencing the measurement It sometimes happens that one or more points of a sounding graph drop out. The resulting curve cannot be smooth. Some of these possible rea- sons shall be explained in the following. 2.2.1. Current electrode wrongly grounded: remain standing When an assistant has not noticed the signal for shifting the electrode and is remained standing, while the other is moved on, then the distance between the electrodes A and B is too short in comparison to the configuration factor K. The K used for calculating ρa is therefore too large. This means, that the apparent resistivity ρa will be too high, i.e. when an assistant is remained standing the point drops out upwards. 2.2.2. Current electrode wrongly grounded: surpassing When an assistant has missed the following L/2 mark after the signal for shifting the electrodes and has surpassed it, then the distance between the electrodes A and B is too large in comparison to the configuration factor K. The K used for calculating ρa is therefore too small. A too small K, however, means that a lower apparent resistivity ρa will be recorded. i.e. when an assistant has surpassed an L/2-mark the point drops out down- wards. 2.2.3. Wire-mesh-fence (Fig.26/27) We assume that a wire-mesh-fence in its lower part touches the ground. With this, a conductive connection to the underground parallel to the measuring range exists. When the electrode reaches the beginning of the wire-mesh-fence, there are still no effects at the sounding graph. But when the electrode passes the wire-mesh-fence and is grounded near to the fence, it seems that the current flows into the ground at the beginning of the fence; that means: when the electrode is shifted from the beginning to the end of the fence, it seems that the electrode effectively has not been moved at all. According to case 2.2.1. the point drops out upwards.
Page 1 and 2: THE SMOOTH SOUNDING GRAPH A Manual
Page 3 and 4: Preface 2 This manual shall be a pr
Page 5 and 6: 1. Basic rules 4 The first chapter
Page 7 and 8: This current density is marked as j
Page 9 and 10: 8 Fig.2 Fig.3 Fig.4 Fig.5
Page 11 and 12: 10 1.3. The four-electrode arrangem
Page 13 and 14: 12 Fig.6 Fig.7 Fig.8
Page 15 and 16: 14 If we compare equations (10) and
Page 17 and 18: Case 2 (Fig. 10) 16 Now we observe
Page 19 and 20: 1.5. The fundamental principle for
Page 21 and 22: Case 3 (Fig.14) 20 The electrode di
Page 23 and 24: with just the same factor K. 22 Aft
Page 25 and 26: 24 Fig17 layers with different resi
Page 27 and 28: 26 Simulating this zooming by enlar
Page 29 and 30: 28 1.6. Shifting of potential elect
Page 31 and 32: 30 Fig.21 Fig.22 Fig23
Page 33 and 34: 32 2.1. How to carry out a field me
Page 35 and 36: L/2 a/2 1,5 6,28 2 11,8 2,5 18,9 34
Page 37 and 38: 36 Fig.27 Fig.28 Before we start th
Page 39 and 40: 38 fence, ditch) especially, if the
Page 41: 40 by experience. The measurement i
Page 45 and 46: 2.2.4. Crossing a ditch (Fig.26/29)
Page 47 and 48: 46 accuracy is not so important the
Page 49 and 50: 2.2.8. Insulation and leakage curre
Page 51 and 52: 50 Fig.31. They are ascending with
Page 53 and 54: 52 If j' is negative, i.e. the dist

THE SMOOTH SOUNDING GRAPH. A Manual for Field Work ... - BGR

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